The present invention relates to perpendicular magnetic recording media and magnetic storage apparatuses, and more particularly to a perpendicular magnetic recording medium and a magnetic storage apparatus capable of performing high density recording.
With rapid development of technology in magnetic storage apparatuses, practical machine of surface recording density of about 100 Gbit/in2 is about to be commercialized by using the technology of in-plane recording, in which recording is made on a magnetic recording medium in an in-plane direction. However, there has been caused the problem of thermal stability of recorded magnetization in the technology of in-plane magnetic recording when the recording unit is miniaturized beyond the recording density of 100 Gbit/in2. While it is predicted that commercialization should be possible up to the recording density of 250 Gbit/in2 with further improvement of technology, it is recognized that the recording density has now almost reached the limit with the technology of in-plane magnetic recording.
On the other hand, with the technology of perpendicular magnetic recording that carries out recording in the perpendicular direction of a magnetic recording medium, thermal stabilization can be secured for the magnetic recording unit by providing an appropriate thickness even when the size of the recording unit is miniaturized. Thus, it is predicted that the surface recording density should be improved to the order of terabit/in2 with the technology of perpendicular magnetic recording.
In the art of perpendicular magnetic recording medium, the mainstream is a so-called dual-layer perpendicular magnetic recording medium, in which there is provided a soft-magnetic backing layer between a magnetic recording layer and a substrate. With such a construction of dual-layer perpendicular magnetic recording medium, a mirroring effect of the soft-magnetic backing layer functions so as to intensify a recording magnetic field from a primary magnetic pole of a recording head, and the recording magnetic head is spatially concentrated to increase the gradient of the recording magnetic field.
On the other hand, the soft-magnetic backing layer disposed against the primary magnetic pole has a spreading, and thus, the magnetic flux exiting from the primary magnetic pole undergoes spreading toward the soft-magnetic backing layer. Thereby, the magnetic flux is diffused at the surface of the recording layer, and there arises a problem that it becomes not possible to form minute recording bits in the recording layer. Because of this, it has not been possible to increase the recording density.
Meanwhile, in anticipation of decrease of reproduced output and increase of medium noise with increase of recording density, investigations are being made for improvement of S/N ratio. More specifically, it is recognized that measures have to be taken for: miniaturization; isolation; orientation control; and improvement of crystallinity, for the magnetic particles constituting the recording medium. Because the magnetic particles of the recording layer are formed on a non-magnetic intermediate layer, the magnetic particles are influenced by the crystal orientation or crystallinity of the non-magnetic intermediate layer, and thus, designing of the non-magnetic intermediate layer becomes an important issue.
When the thickness of the non-magnetic intermediate layer is increased for improving the crystallinity of the non-magnetic intermediate layer, there arises a problem in that, although the crystallinity of the recording layer is improved, the spacing between the recording head and the soft-magnetic backing layer is increased, leasing to further spreading of the magnetic flux.
Patent Reference 1
Japanese Laid-Open Patent Application 2002-163819 official gazette
Patent Reference 2
Japanese Laid-Open Patent Application 3-130904 official gazette
Patent Reference 3
Japanese Laid-Open Patent Application 6-295431 official gazette
Patent Reference 4
Japanese Laid-Open Patent Application 10-3644 official gazette
Patent Reference 5
Japanese Laid-Open Patent Application 2001-134918 official gazette